Paypal is not overriding the return URL?

I need to override the given default Auto return URL from the paypal button HTML code. I followed these steps:

1. Check the Auto return Url section and gave a default URL
2. Generate a Buy Now button and left the Return and Cancel URL options as it is.

3. Paste the button code

   <form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
   <input type="hidden" name="return" value="http://www.someURL.com"/>
   <input type="hidden" name="cmd" value="_s-xclick">
   <input type="hidden" name="hosted_button_id" value="G3WQ*******">
   <input type="image" src="https://www.sandbox.paypal.com/en_GB/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal – The safer, easier way to pay online!">
   <img alt="" border="0" src="https://www.sandbox.paypal.com/en_GB/i/scr/pixel.gif" width="1" height="1">
   </form>
   

After successful payment on Sandbox PayPal is always redirecting me to the default URL.

Why isn't overriding it? Any help would be appreciable.

I saw a couple of similar unanswered question on PayPal community and StackOverflow as well:

• https://www.paypal-community.com/t5/About-Payments-Archive/Auto-Return-Custom-URL-Not-Overriding-Auto-Return-Setting-URL/td-p/1038334
• Paypal button auto-return url not overriding the default url
• Setting PayPal return URL and making it auto return?